dew-point detecting device



Feb. 7, 1956 l. slLvL-:RMAN

DEW-POINT DETECTING DEVICE Filed D66. 16, 1953 REFRWERATOR DEW-POINTDETEC'IING DEVCE VThis invention relates generally to dew-pointdetecting devices and more particularly it is concerned ywith apparatusfor visually detectingv the dew-point in a manner which will render thesaid apparatus accurate and reliable.

The invention comprises a variation of the invention described andclaimed in a co-pending application entitled Dew-Point Measuring Deviceand Method, Serial No. 251,2137led October 13, 1951, by Edwin W. Donathand assigned to the same assigner as the application herein.

ln the said co-pending application, the dew-point was determined byproducing a contrasting appearance between wetted and unwetted surfacesof a moisture collector, the collector being roughened so as to provideinterstices and pits into which the moisture collected to provide avariation in the appearance ofthe surface in reflective light.

At the dew-point, the localized portion of the surface would becomewetted and retiect light instead ofscattering the same so that the spotbecome darker in appearance.

In order to achieve the required contrast, the said c ollector comprisedsome member of glass or the like having a roughened top surface andhaving a localized cooling member engaged against its lower surface toconcentrate the cooling.

This invention differs from that of the said co-pending applicationprincipally in that the cooling of the collector need not be localizedin order to achieve the contrast and hence any refrigeration means couldbe used to be applied to the entire bottom surface of the collector ifdesiredbut the results achieved are substantially of the sameor asimilar degree of accuracy.

4It is the general object of the invention to achieve the manyadvantages as set forth in the prior application, but only generally andin emphasis of the objects of the said invention. It is the primaryobject, with reference only to this invention ,to provide adew-pointdetermining device ,in which no localizedcooling ofthecollector is required in order to achieve accurate and reliable resultsthrough the use of simple and economical means easily operable bypersons of ordinary skill.

Still a further object of the inventionis to provide a n dew-pointdetecting device in which there is a moisture collector, the bottom ofwhich is subject torcooling over a relatively large area, but thesurface of which is roughened only in a predetermined smaller area sothat when the dew-point occurs the contrast between the roughened andunroughened area will be heightened, by the roughened area becoming wetand light reflective in' character.

Still a further object of the invention is to provide dewl pointdetermining apparatus of the character described in which the surfaceofthe colletoror the back thereof is treatedto produce contrasting areaswhich exist as such when dry, but which lose their contrastingappearance when one of the said areas becomes wet at the dew-point.

Still a further object of the invention is to provide a dew-pointdetecting apparatus of the character described in which contrast or lackof contrast between the two areas described in the immediately abovereferred to object is achieved by means of pigment.

nited States Patent YO "ice Still a further object of the invention isto provide a dew-point detecting apparatus in which the contrast or lackof contrast referred to is achieved by means of light.

Many other objects will appear and advantages become apparent as thedescription of the invention proceeds in connection with whichdescription there has been set forth in considerable detail theconstruction and operation of preferred embodiments of the invention.The same are likewise fully illustrated in the attached drawings asrequired by the patent laws.

In the drawings:

Fig. l is a sectional view through an apparatus constructed inaccordance with the invention, the same being shown more or lessdiagrammatically utilizing representations for structure which arewell-known to those skilled in the art.

Figs. 2, 3 and 4 are respectively diagrammatic Views of different formsof the collector member of the invention, the iirst two beingperspective views and the last being a sectional view. All of the views.are exaggerated as to dimensions in order to illustrate variousfeatures of construction and arrangement.

in Fig. l there is illustrated apparatus in diagrammatic form as stated,the same consisting of a dew-point measuring device 10 including ahousing 11 of insulating material mounted adjacent or immediately upon arefrigerator 12 of any suitable construction. It will be recalled in theco-pending application above referred to that the refrigerating meansrequired a localized cooling of the collector. This is not alwayspractical, either economically or structurally, especially where somecooling means is available remote from the apparatus. There isillustrated a cooling chamber 14 formed by a metal diffusing cylinder 15whose cap end 16 engages against the bottom` of the collector member-1S.Any refrigerating means which will provide a cooling effect upon arelatively large area of the collector 13 is considered within the scopeof the invention, and hence it is pointed out that the refrigerator 1.2with its coolant carrying coils 20 inside the cylinder 15 areillustrated merely by way of example.

The housing 11 has a cavity 22 formed in the top thereof and within thiscavity there is inserted the collector 1S, which of course must be ofthe same shape and size as the cross section of the cavity. Obviouslyfor those collectors illustrated in Figs. 2 and 3 the cavity would haveto be cylindrical. The collector 18 is at the bottom of the cavity 22and va retaining barrel 24 of insulating material preferably is engagedupon the collector 18 to hold the same in position. Inlet and outletports 26 and 27 of the barrel24 are readily aligned withu the inlet andoutlet gas;

or vapor conduits 28 and 29 which pass through the side walls of thehousing 11. The valves Sil and 31 may be provided in the conduits torender the gas admitted to the chamber 32 quiescent if desired. SuchVvalvesmay be omitted and the barrel rendered revolt/ able in whichcase. a rotation of the same bridging the ports 26 and 27 out ofalignment with theconduit ends will entrap a sample' of gas. t

The upper end of the barrel is closed oif by a suitable sight glass 34which in turn may be covered by alight" lter 35 as will be describedhereinafter. A thermocouple 36 having leads38connecting same toatemp'era'tureindieating potentiometer or galvanometer dtlcompletesftheV apparatus, except for the specic description of the collector 1Swhich is the heart of thedevice. i

It will be noted that there is a localized roughened" note a great andmarked increase in contrast at the dewpoint. He notes the temperatureindicated by the instrument 40 at that instant and has an accurateindication of the true dew-point.

The dew-point as referred to herein signifies the actual physical pointwithout regard to methodv of determination at which the vapor or gasfirst changes state so that the first molecules of liquid vapor areproduced. This may be slightly before the actual instant of detection bythe apparatus, but it is believed that through the use of the inventiondeterminations are obtained which are more accurate than those possiblethrough the use of known apparatus requiring the visual powers of anobserver.

They reason for the increase in contrast is that the light whichheretofore was scattered by the roughened spot is now reflected in adiierent manner through the water filling in the interstices, pits andvalleys of the roughened spot. This is the first moisture condensed uponthe carrier, since the peaks of the roughened spot tend to seed thevapor while the smoother portions 4l) tend to cause the vapor occurringover such smooth areas to retain a super-saturated condition until longafter the dew-point is reached. If the lowering of the temperature iscontinued obviously dew or fog will eventually appear upon the smoothsurfaces as Well.

The lack of contrast between the roughened and smooth areas 39 and 46may be heightened through the use of light of various colors. VTheiilter is shown to provide such color eiects. projected colors mayaccomplish the same purpose.

A modified form of the invention is shown in Fig. 3. Here instead ofdecreasing the contrast when the collector 18'is dry it is increasedthrough the use of die or pigment on the surface as indicated atl 42.The spot 43 is not so treated. Thus, for example, suppose the apparentcolor of the spot 43 when wet is a certain shade of grey or blue,depending upon the material from which the collector is made. Thecollector surface is painted or dyed that precise color in annularformation about the spot 43 so that the observer when looking throughthe sight glass 32 will see a great contrast. He can obviously note theuncolored spot in the center. Then as the temperature is reduced, at agiven point the spot 43 will suddenly darken like its surroundingannulus 42 and blend thereinto. This marks the dew-point, since themoisture caught by the roughened surface will darken that surface to thecolor of the remainder of the collector. In this case it is preferredthat the spot 43 be rough and the other portion 42 smooth but this isnot essential.

In Fig. 4 there is illustrated a collector 18 which is translucent sothat the pigment or dye 44 can be applied in an annulus to the bottomsurface leaving the center spot 45 on the top surface untreated.

Light can also be used in connection With the modications of Figs. 3 and4 to heighten or lessen the contrast as desired.

It is pointed out also that the collector itself may be formed of somecolored material which will either enhance or reduce the contrast forthe purposes described. Likewise, the light can come either from thetop, side or bottom depending upon the construction and materials used.

Variegated colors or aligned It is believed that the invention has beenfully explained such as to enable those skilled in the art to which thesame appertains to construct the apparatus and use the same, and it isdesired to be limited as to variations and changes only insofar asthescopeof the invention is limited by the claims appended hereto.

What is claimed is:

l. A dew-point ,detecting device which operates by providing an opticalchange in a surface area, which comprises a housing having a chambertherein, means for leadinga gas sample into said chamber, a moisturecollector in said chamber having a surface exposed to said gas sample inthe chamber, means cooling substantially all of said surface whereby tolower the temperature of the gas at the said surface, means formeasuring the temperature of the deposited condensate when the dew pointof the gas is reached, said surface having two portions of predeterminedoptical contrast relationship when both portions are dry, .but producinga visible change in said optical contrast relationship when one of saidportions is wetted at the dew-point, said one portion having meansrendering the same light-scattering in character Y when dryk andnon-light-scattering in character when wet,

the second portion being non-light-scattering in character whendry, saidone portion of said surface having a rough texture provided withinterstices and peaks whereby to provide an encouragement of moisturedeposition on said one portion, and said second portion is of texturesubstantially smoother than that of said one portion and inhibiting thedeposition of moisture thereon.

2. A dew-point measuring device which comprises a housing having achamber therein and means for leading a gas sample into the chamber, aplanar moisture collector closing oif a side of the chamber andpresenting a face to the chamber, refrigeration means on the oppositeface of said collector cooling the collector and lowering thetemperature of the gas impinging against the face presented to thechamber, the exposed face being pigmented except for a local part, saidpart having a roughened surface to enable the seeding and capturing ofmoisture condensed out of said gas, the color of the pigmented portionbeing substantially the same as that of the roughened part but only whensaid roughened part is wetted, and being of contrasting color relativethereto when dry, whereby when the dew-point is reached and moisturedeposited upon the roughened part, the entire exposed face will assume asubstantially homogeneous hue. v

3. A dew-point meter as described in claim l in which said moisturecollectorV has pigment applied thereto of a character substantially todecrease the color contrast between the roughened portion when Wet andthe smooth portion when dry such that upon deposition of moistureuponrthe roughened portion the same will substantially blend with thesmooth portion and appear to disappear to an observer.

4. A dew-point meter as described in claim 1 in Which the moisturecollector is illuminated as to the smooth portion by means of coloredlight of substantially the same color of the roughened portion when wet,whereby to cause apparent substantial blending of the roughened portionwhen wet.

1,883,116 Tomlinson Oct. 18, 1932 2,593,313 Kamm et a1 Apr. 15, 19522,697,933V Donath Dec. 28, 1954

